1. Field of the Invention
The present invention is related to an axial drag regulator for large-volume radial compressors, including an axial diffusor with a ring of guide vanes extending axially with respect to the axis of the charger and being rotatable around radially extending rotatable axle shafts. The guide vanes are substantially circle sectors of such a shape and pitch that, when the diffusor is totally closed, they nearly cover the total cross section of a flow channel which is formed within a casing. The inner wall of the casing, when seen in the flow direction, comprises a first barrel of a first cylinder section and a barrel of a spherical section, the spherical radius of such spherical section being equal to the radius of the first cylinder section, and the spherical section transitioning smoothly, nozzle-like, into a second cylinder section. Adjusting levers are disposed along the axle shafts of the guide vanes and project outward and extend along the axes of rotation of the guide vanes. The adjusting levers are coupled to an adjusting ring concentrically enclosing the casing.
2. Description of Background and Other Information
Such an axial drag regulator is disclosed in German Patent No. 1,628,232 for large volume compressors and serves to shift the characteristic curve. In such known axial drag regulator, the flow channel in which the guide vanes of the axial diffusor are disposed, includes two barrel sections having only slightly different diameters, and a spherical section between the two barrel sections The diameter of such spherical section is larger than the diameter of the larger cylinder barrel section, i.e. the diameter of the flow channel on the intake side increases in the guide vane region. Such diameter increase in the flow channel causes turbulence and flow separation and an increase of the vortex trail triggered by a velocity jump at the guide vanes. Since the cylinder barrel section adjacent to the spherical section on the compressor side has an only insignificantly smaller diameter than the first cylinder barrel section, a fast suppression of the flow disturbances prior to entering the compressor is not possible, in particular, because the compressor is located in close proximity to the axial drag regulator.
U.S. Pat. No. 1,978,128 discloses an axial drag regulator in which the guide vanes of the axial diffusor are disposed in a housing which transitions from a larger diameter to a smaller diameter by way of a polygonal housing. The rotatable axle shafts of the guide vanes are inclined at a certain angle with respect to the longitudinal axis of the flow channel and are guided in the center of the flow channel in a gear unit which causes a considerable disturbance of the flow. The various guide vanes are coupled by the gear unit in order to guarantee synchronism. The end of the rotatable axle shafts of the various guide vanes opposed to the gear unit is supported approximately in the center section of the polygonal housing, so that the leading edges of the guide vanes extend approximately perpendicularly with respect to the center line when they are in the completely opened condition. Due to the polygonal shape of the housing wall, the gap between the guide vanes and the barrel face may be kept relatively small when the guide vanes are in their completely open condition; however, considerably large gaps appear both at the leading edge and the trailing edge when the vanes are slightly rotated in the direction towards the closed position, as is usual in normal operating conditions, the gaps causing a turbulence of the flow which causes a vortex trail which cannot be suppressed before it reaches the adjacent compressor.
In European Patent No. 243,596, an axial drag regulator for an exhaust gas turbo-charger is disclosed. A spherical section is contiguous to the first cylinder section of the flow channel, which transitions like a nozzle into a second cylinder section, and at the same time into the intake section of the exhaust turbo-charger. This nozzle-shaped spherical section causes a steadying of the flow behind the axial diffusor; in particular, because of the relatively large diameter relation between the intake cylinder section with respect to the output cylinder section. In such an axial drag regulator for exhaust turbo-chargers, the rotatable axle shaft of the respective guide vanes is disposed within the trailing edge of the vane. This one-sided bearing of the guide vanes causes the appearance of relatively high flow forces which, in the case of axial drag regulators for large-volume compressors, not only are undesirable but necessitate very expensive constructional measures.